1. Field of the Invention
The present invention relates to a cerium oxide slurry, a cerium oxide polishing slurry, and a method of polishing a substrate using the same.
2. Description of the Related Art
In recent manufacturing process of ULSI semiconductor devices, various processing technologies for higher density and finer size are researched and developed. One of them is CMP (chemical mechanical polishing) technology, which is now an indispensable technology in manufacturing process of semiconductor devices for flattening of interlayer dielectrics or BPSG films (silicon dioxide film doped with boron or phosphorus), isolation and forming of shallow trench devices, and forming of plugged and embedded metal wiring.
Conventionally, in manufacturing process of semiconductor devices, inorganic dielectrics layer such as silicon oxide insulation film are formed by plasma CVD or low-pressure CVD method. As chemical-mechanical polishing slurry for flattening the inorganic dielectrics layer, a fumed silica polishing slurry is generally used. The fumed silica polishing slurry is prepared, for example, by growing the grains by pyrolysis of silicon tetrachloride, and adjusting the pH.
However, such fumed silica polishing slurry is low in polishing speed.
In the generation after Design Rule 0.25 μm, shallow trench isolation is employed in isolation of devices in integrated circuits. In shallow trench isolation, CMP is used for removing excess silicon oxide films formed on the substrate. A stopper film of small polishing speed is formed beneath the silicon oxide film in order to stop polishing. The stopper film is made of silicon nitride or the like, and it is preferred that the polishing speed ratio between the silicon oxide film and stopper film may be greater.
However, the polishing slurry of colloid silica composition is small in the polishing speed ratio between the silicon oxide film and stopper film, being about 3, and so far from practical property for shallow trench isolation.
On the other hand, cerium oxide polishing slurry is used as polishing slurry for glass surface such as photo mask or lens. Cerium oxide particles are lower in hardness as compared with silica particles or alumina particles. Therefore, the polishing surface is hardly scratched, and this solution is useful for mirror smooth finishing. Moreover, the polishing speed is faster than silica polishing slurry.
When the cerium oxide polishing slurry for glass surface polishing is directly used in polishing of inorganic dielectrics, however, primary particle size of cerium oxide is too large, and the insulation film surface may be scratched. Recently, a cerium oxide polishing solution using cerium oxide abrasives adjusted uniformly in primary particle size is proposed (see, for example, Japanese Patent Application Laid-Open No. 10-106994).
Coarse grains of cerium oxide particles are also known to cause scratches, and a composition limited in coarse grain amount is proposed (see, for example, Japanese Patent Application Laid-Open No. 2003-171653).